Chestburster in Aliens
Two different Chest-bursters were created for Aliens - one, inarticulated, used for actually bursting through synthetic chests and another one a fully articulated replacement to be used after the creature emerges from its victim. One of the Stan Winston's crew sculpted the Chest-burster before it was shipped to London.
The second shot of this video is the test performed by the effects crew of the articulated Chest-burster's inner skeleton.